1. Field of the Invention
The present invention relates to a vehicle headlight, and more particularly to a poly-ellipsoid system (PES) vehicle headlight capable of compensating for light intensity of a dark region.
2. Description of the Related Art
When vehicles run on the road, to accommodate different traffic situations and visual demands, vehicle headlights may be classified into high-beam headlights, low-beam headlights, and vehicle headlights capable of being switched between the high-beam headlight and the low-beam headlight, and recently the design applied to the vehicle headlight is called a poly-ellipsoid system (PES) vehicle headlight. Referring to FIG. 1, it is a PES vehicle headlight serving as the low-beam headlight. The PES vehicle headlight includes a reflector 61 defining an accommodation space 610, a light source 62 installed in the accommodation space 610 and disposed along a horizontal optical axis X, a light shield 63 extending upwards from a bottom edge of the reflector 61 and having a top edge height the same as an optical axis X, a shell (not shown) assembled on a front side of the reflector 61, and a lens 64 installed on the shell. Light rays emitted from the light source 62 are reflected by the reflector 61 and shielded by the light shield 63, such that after passing through the lens 64, the light rays are mainly emitted horizontally or slightly downwards towards the region under the optical axis X, thereby achieving effects of the low-beam headlight. Although the vehicle headlight may be used as the low-beam headlight, the light rays are mainly scattered in a region under the optical axis X, such that the region above the optical axis X has an insufficient light intensity, and thus the region is hereafter referred to as a dark region. Generally, the light intensity of the dark region approximately more than 18 meters in front of the vehicle headlight should be at least 64 candelas (cd), but the dark region of the conventional vehicle headlight has distinctly insufficient light intensity, such that when driving the vehicle at night, the driver cannot clearly read traffic signs disposed on higher positions on the road.
Referring to FIG. 6, it is a distribution view of a light field of a position 25 meters in front of the light source 62 of the conventional vehicle headlight. In the diagram, a horizontal axis represents the horizontal angles of the left and right sides at the position 25 meters in front of the light source 62 serving as a center, a left vertical axis represents upper and lower angles, and bottom graduations represent the light intensity represented by each line (in a unit of cd). It can be obtained from FIG. 6 that the dark region has nearly no light rays, such that the light intensity value thereof cannot meet the requirements of the rules.
The insufficient light intensity in the dark region may affect safety during driving, so recently many designs for compensating for the light intensity in the dark region of the low-beam headlight were proposed. Referring to FIG. 2, for example, in U.S. Pat. No. 6,736,533, in the vehicle headlight of the prior art, an auxiliary shielding board 72 is added on a front side of a light shield 71, and the auxiliary shielding board 72 may reflect a part of the light rays emitted downwards, such that after passing through the lens 73, the light rays form compensation light rays A1 refracted upwards and are emitted, thereby compensating for the light intensity in the dark region. Referring to FIG. 3, in the US patent, a perforation 810 is opened on a light shield 81, and an auxiliary shielding board 82 is disposed on an inner side of the light shield 81, such that light intensity in the dark region is compensated through the modified structures.
On the other hand, some vehicle headlights can be switched between the high-beam headlight and the low-beam headlight, in which case, an electromagnetic valve is used to drive a modulatable light shield to rotate, thereby changing an outward projecting path of the light rays, so as to switch between the high-beam headlight and the low-beam headlight. However, the light shield 71 and the auxiliary shielding board 72 are combined in a link-up manner, and the perforation 810 is disposed on the light shield 81. The structural modification of the light shields 71 and 81 may compensate for light intensity of the dark region, but the demands of the high-beam headlight cannot be met. Therefore, the above design for compensating for light intensity in the dark region is applied to only the low-beam headlight, and cannot be applied to the vehicle headlight capable of being switched between the high-beam headlight and the low-beam headlight. Therefore, the design applicability is poor, and needs to be modified.
In addition, in U.S. Pat. No. 6,494,603, the light shield disposed in front of the light source is used to compensate for light intensity of the dark region, but the light shield and a supporting case are integrally formed by casting. During casting, the accuracy must be improved; otherwise, after the light shield is shaped, the disposition angle easily generates deviation, such that the light rays cannot be reflected to a preset direction. Moreover, the design cannot be applied to the vehicle headlight capable of being switched between the high-beam headlight and the low-beam headlight.